Apparatus for tightening electrode joints



June 29, 1943. F. w. BROOKE l APPARATUS FOR TIGHTENING ELECTRODE JOINTSFiled June 27, 1940 4 Sheets-Sheet l m .7 W WA:

r. K Rm Y m Wm WM am M fi m 4 Sheets-Sheet 2 I HIIHIH H II 1 I I v F. W.BROOKE APPARATUS FOR- TIGHTENING ELECTRODE JOINTS Filed June '27, 1940June 29, 1943.

ATTORNEY J1me 1943- F. w. BROOKE ,32 ,918

APPARATUS FOR TIGHTENING ELECTRODE JOINTS Filed June 27, 1940 4Sheets+Sheet 3 INVENTOR F/rmv/r M fi/rooxf gjadfdl ATTORNEY June 29,'1943. 2,322,918

F. W. BROOKE APPARATUS FOR TIGH'IENING ELECTRODE JOINTS Filed June 27,1940 4 Sheets-Sheet 4 INVENTOR Ffifl/V/f M 5/?00/(6 .0000! BY I I I I II I I000 2000 3000 4000 5000 6000 F0 OT-POU/ DS OPQUE I @W AT ORNEYPatented June 29, 1943 UNITED STATES PATENT OFFICE Frank W. Brooke,Pittsburgh, Pa., assignor to Swindell-Dressler Corporation, Pittsburgh,Pa., a corporation of Pennsylvania Application June 27, 1940, Serial No.342,657 3 Claims. .(Cl. 29-84) The general object of the presentinvention is to provide an improved method of and apparatus fortightening the threaded coupling connections between end to end sectionsof carbon furnace electrodes, so as to eliminate objectionable electrodejoint resistance.

The use of electric arc furnaces for iron and steel melting and othermetallurgical and chemical purposes, is extensive and continuouslyincreasing. In such furnaces, the electrodes are rod-like bodies,usually circular in cross section,

of' carbon in amorphous, semi-graphitic, or graphitic form. Suchelectrodes vary in their dimensions with the character of the furnace inwhich they are used and the conditions of use, from a diameter of aboutfour inches up to a diameter of forty inches. The individual electrodesections customarily vary in length from forty inches to one hundred teninches. In iron and steel melting furnaces, the electrodes employed areordinarily of the order of eighteen inches in diameter and six feet inlength.

' In most cases, each furnace electrode in use, consists of two or moreelectrode sections connected end to end. In use, the arcing end of afurnace electrode is constantly wasting away, so that it is necessaryfrom time to time at relatively frequent intervals to add a new sectionto the outer end of the electrode. The end to end electrode sections areconnected, in standard practice, by nipples or plugs formed of the samematerial as the electrode sections, and having end portions oppositelytapered and externally threaded to screw into internally threadedtapered sockets formed in the ends of the electrode sections.Heretofore, it has been customary to tighten up the threaded connectionbetween the outer electrode section previously in use, and a sectionbeing added, by the manual actuation of a wrench or analogous implementattached to the last mentioned section. In practice, the maximum jointtightening torque used in thus tightening an electrode joint customarilyamounts to some three or four hundred foot pounds, in the case of anelectrode 18" in diameter and of the usual construction.

I'have discovered that it is practically feasible and desirable toemploy an electrode joint tightening torque and contact pressure muchgreater than those heretofore customary, and that it is thus possible togreatly reduce the electrode joint resistance and joint temperatures,and thereby increase the furnace efficiency and materially reduce thetendency tobreakage of the electrode portions Within the furnace.Specifically I have found, for example, that a standard graphiteelectrode eighteen inches in diameter will have a joint resistance whenthe joint tightening torque is three hundred foot pounds, which is aboutfour times the joint resistance when the joint tightening torque isthree thousand foot pounds.

The importance of joint resistance increases with the amount of currentflow through the electrode. There is a constant tendency in the industryto increase the electrode current flow.

Electrode joint resistance necessarily results in an electrodetemperature higher at the electrode joints than in the body of theelectrode and the difference in many cases is sufiicient tosignificantly increase the rate of electrode oxidation and therebydecrease the electrode cross sectional area at the joint. The evileffectsof the oxidation due to high joint resistance. are thuscumulative. Electrode joints not only increase electrode resistance andthereby reduce furnace efficiency, but they ordinarily reducethe'lectrode strength, and in particular they reduce the capacity of theelectrodes to withstand the enormous electromagnetically produced,vibratory stresses to which they are subjected as a result of theconstantly occurring load condition changes. Those stresses tend toloosen the joints and thus increase the joint temperatures. and therebyfurther impair the joints, so that from time to time an electrodesection below a joint within the furnace chamber breaks away from theelectrode. This not only involves objectionable electrode wastage, butdisturbs the furnace operation and in some metallurgical operations, theaddition of the carbon electrode section to. the

molten bath may disastrously effect the value" of the furnace charge. iv

A major object of the invention is to provide a practical method of andmeans for subjecting electrodes to joint tightening forces much higherthan have been customary heretofore.

A more specific but practically important object of the invention is toprovide a method of and means for adding an electrode section to .anelectrode installed in a furnace and to subject the connecting joint toa tightening force of the relatively great magnitude characteristic ofthe present invention which will require no modification of, or additionto existing furnace structures and which will not subject the furnacestructures to objectionable stresses or operating conditions. Myinvention is characterized by the simple provisions made whereby intightening the joint between the outer end section of an electrodemounted in a furnace and a section to be added thereto, each of the twosections is subjected. to a torque opposite in direction andsubstantially equal in magnitude to the frictional resistance torquewith which each of said sections opposes turning movement relative tothe other section.

Furnace dust or other dirt in an electrode joint tends to a greatincreasein joint resistance and a materialreduction in the strength ofthe joint and in its capacity to stay tight. A specific object of thepresent invention is to provide the joint tightening device which I havedevised. with, simple and effective means for cleaning joint formingsurfaces, and particularly the upper end of the furnace electrode towhich a section is tobe added, by compressed air jets. My improved jointtightening device may include power multiplying provisions enabling aman to subject. the. electrode sections to joint tightening torques ashigh as are required, but where conditions make this desirable, myjointtightening device may include a suitable motor supplying the jointtightening power.

The various features of novelty which. charact'erize. myinventionarepointed out with particularity in the claims annexed to and formingapart of this specification. For a better understanding ofthe-invention, however, its advantages, andspecific objects attained.with its use, reference should be had to the accompanying drawings anddescriptive matter in which I have illustratedv and described apreferred embodiment of the invention.

Of the drawings:

Fig. 1 is a diagrammatic representation of a plant comprising anelectric furnace, and associated apparatus for adding sectionsto the furnace electrodes as the latter waste away:

I Fig. 2 is an elevation on an enlarged scale of. a portion of theelectric furnace shown in Fig. 1 and also shows a preferred. form of myelectrode joint tightening device;

Fig. 3 is an elevation, partly in section,.of an electrode section andasupport on which the section. is mounted preparatory to its connectionto my electrode joint tightening device;

Fig; 4 is a view showing my electrode joint tightening device inoperative relation with the electrode section and'support shown in Fig.3;;

Fig; 5 is a somewhat diagrammatic representationof screwthread relationsof an electrode section coupling parts and of the joint tighteningdevice,,in an intermediate stage of an electrode section couplingoperation; Fig. 6 illustrates the screw thread relations 0 the electrodesection coupling parts in a final stage of an electrode section couplingoperation;

Fig. '7 is a large scale reproduction, with parts broken away and insection, of aportion of Fig. 2;

Fig. 8 is a sectionon theline 8.8 of Fig. '7;

Fig. 9 is a section on the line 9-9 of Fig, '7;

Fig. 10- is an elevation'of a motor actuating torque tightening device;and

Fig. 11 is a curve illustrating the reduction in electrode jointresistance effected by increasing the joint tightening force.

In the drawings'I'have illustrated the use of the present invention inconnection with a conventionally illustrated electrical arc furnace A ofwell known type, comprising three electrodes B extending into thefurnace chamber through openings in its roof, and each supported forlongitudinal adjustment by an individual gallows element 0. Each of thelatter comprises ahorizontal arm with a clamp C at one end forencircling and gripping the corresponding electrode B, and having itsother end connected to a vertically movable plunger C The latter, whichis mounted in a vertical guideway, is customarily supported and givenvertical adjustments by a winch operated by a reversible electric motorautomatically controlled by means responsive to the voltage drop in theare between the electrode and the charge, to raise or lower theelectrode as required to maintain the arc voltage drop approximatelyconstant. The current carrying connection D to each electrode ismechanically supported by the corresponding gallows member C. Theconstruction details of the members C and the mechanism by which saidmembers C are guided and vertically adjusted, need not be illustrated,or further referred to herein, as they form no part of the presentinvention and may be of well known form.

Each of the electrodes B comprises a plurality of similar sections 1)connected end to end. Each section b is formed at each. end with atapered internally threaded socket b; and the two adjacent sections b ofeach electrode are connected by a nipple or pin 11 having its two. endportions oppositely tapered and externally threaded to screw into theadjacent end sockets b of two adjacent electrode sections 1). Aspreviously indicated, the electrode sections 1) are ordinarily formed ofcarbonin amorphous, semi-amorphous or graphitical form, and may widelyvary in diameter and length, to adapt them for use in furnaces ofdifferent sizes and for different furnace conditions of use. Ordinarilythe nipples or pins 1) are formed of the same material as the electrodesections b which they connect.

In use, each electrode B is constantly wasting away at its lower end,and from time to time a new section I) must be added to the upper end ofthe electrode. Preparatory to the addition to an electrode of anelectrode section b, the first step, ordinarily, is to thread a taperedlifting or suspension plug E into the socket b at one end of thesection, and to thread a nipple or connecting pin b into the socket b atthe opposite end. of the section. The member E is provided with an eye Eadapted for engagement by the hook F of a crane or hoist, which afterbeing entered in the eye E, is operated to upend the section b and liftit off such a stock pile as is shown at the left hand side of Fig. 1,and to then move the section b into'a position above and into engagementwith the support G as shown in Fig. 3.

The support G, as shown, comprises a base portion and a central portionG cylindrical in outline and extending up from the base portion. Theportion G is formed with a cylindrical cavityopen at its upper end andadapted to receive a nipple or pin b threaded in the socket of the lowerend of a section b, standing on the horizontal upper end surface of theportion G of the support G. As shown, a tubular metal sleeve or thimbleG surrounds the support portion G, and extends upwardly above the upperend of the latter to provide a socket or guide which assists in ensuringthat each section b supported by the support G, is properly centeredthereon. While the section b is resting on the support G, as shown inFig. 3, the suspension plug E is removed, and the joint tighteningdevice H is moved into operative relation with the electrode section andis clamped to the latter.

The device H, as shown in detail in Figs. 7, 8 and 9, comprises a bodyportion beneath an upper suspension section HA, and above upper andlowerelectrode clamping sections HB and HC. In the. preferred form shown, thedevice H is U shaped orarc shaped inv cross section, so that it may belaterally moved into the position in which its clamps are in position toengage an electrode, or electrode section, at points of the electrodesurface extending around the electrode axis for considerably more than180, so that when the clamps are tightened on an electrode section, thelatter and the tightening device are positively centered, relative toone another. The suspension section HA comprises an upper internallythreaded tubular part or nut H coaxial with an electrode section engagedby the device H. An externally threaded suspension bolt H is threadedinto the nut H, and is provided at its upper end with an eye H forengagement by the hook F of the crane or hoist employed to move andsupport the device H. The suspension part HA includes three dependingarms H each bolt-connected at its lower end to a corresponding uprisingarm H The body portion of the tightening device in the preferredconstruction shown is a metallic tank, U shaped in horizontal crosssection and adapted to hold in its reservoir space h air under pressurefor use in cleaning electrode joint surfaces, and provided with a valvedinlet H and valved outlet H". The arms H are connected'to the upper endof the tank structure, and arms H secured to and depending from thelower end of the tank structure, are bolted or otherwise detachablyconnected to corresponding uprising arms H of the upper clamping sectionHB.

' .The clamping section HB comprises an arcshaped body portion or clampframe, having ratchet-like teeth H distributed along a central innersideportion and adapted to bite into and grip the electrode section engagedby the device H. To each end of the body portion of the clamping sectionHB, a corresponding clamping lever I is pivotally connected by a pivot1'. Each lever I comprises an outer handle portion by which ratcheteliketeeth I at the inner end of the lever may be brought into grippingengagement with the electrode section. As shown, the toothed inner endof each lever I is cam. shaped so as to engage and bite into theelectrode section with increasing pressure as the lever isturned in theclockwise direction as seen in Fig. 8. As shown, the ratchet-like teethI and H are each inclined in the direction required for biting movementof its end edge into the electrode section b, when the clamping sectionHE is subjectedto a torque tending to give it a clockwise rotation aboutthe axis. of the electrode section. As will be understood, the teethHand H are inclined and the inner ends of the lever I are shaped asdescribed on the assumption that the screw threads on the parts b, b; Hand H are all right hand threads.

--'I-'he clamping section'I-IB comprises depending arms H havingishouldersH at their ends,

which extend beneath and support arc-shaped flanges H on an uprisingportion H of the lower clamping section H0. The sections HB and HC arereleasably secured against radial displacement, by a part H bolted tothe section H0 and overlapping the central arm H The section HC includesteeth H and clamping levers J, respectively similar to the teeth H andlevers I of the section HB, except that the inner cam ends of the leversJ are shaped, and their teeth J and the teeth H are inclined to biteinto and grip an electrode section, when the clamping section HC issubjected to a torque tending to give it acounterclockwise rotationabout the electrode axis.

The support G and the tightening device H are formed and proportioned toposition the tightening device in, predetermined longitudinal relationto an electrode section I) supported on the portion G of the support G.To this end, the support G is formed with a horizontal annular surface Gsurrounding the lower. end of the portion G, and forming a seat engagedby the bottom of the clamping section HC, and thereby supporting thedevice H in the proper longitudinal relation with the electrode sectionsupported on the support portion G. In that relation the clampingsection HC is suitably below the electrode section b, and the clampingteeth H and I engagethe electrode section at a level slightly below theupper end of its lower end cavity b, where suitably heavy tighteningstresses may be applied to the electrode without risk of injury to thelatter.

After the tightening device H is properly positioned with respect to theelectrode section b resting on the support G, and the levers I areadjusted'to positively clamp said section in the device H, the crane orhoist is manipulated to move the tightening device H and the electrodesection b clamped therein, ofi the support G, and into the positionshown in Fig. 2, in which said section b is in alignment with and abovethe upper end of the electrode B; to which the section b is to be added.The crane is then lowered far enough to enter the tapered lower endportion ofthe pin or nipple b of the section b' held by the device H, inthe socket b' in the upper end of the electrodeB, but not low enough tobring the threads of said pin and socket into crushing engagement.

The tightening deviceH is then rotated clockwise about the electrodeaxis, as by manual force applied to the handles of the levers I. Thisresults in a relative rotation of the nut H and bolt H which lowers thedevice H and the elec trode section b which it supports. As thisrotative and lowering .movement of the device H progresses, the threadonthe tapered lower end portion of the pinor-nipple b of the section bheld in the device H, comes into operative engagement with the Wallthread of the socket b" at the upper end of the corresponding electrodeB as shown in Fig. '7. The rotative movement ofthe device H is normallycontinued until the lower end of the electrode section b held in thedevice H, abuts directly against the upper end of the subjacent sectionof the electrode B. 1 In ordinary practice, after the initial torqueapplied to the device H has started the latter into rotation, therotation is continued by the momentum of the device and the electrodesection b which it supports, until arrested by the frictional en-'gagement ofthe end surface of said section with the upper end of theelectrode B.

, In the preferred form of the invention, the thread pitch of thesimilar threads on the inner wall of the sockets b and on the pins ornipples 12 is coarser than the-thread pitch of the nut H and suspensionbolt H by apredet'ermined amount of pitch difference is that required toraise the outer edge of the thread rib on the pin b relative to thebottom of the thread groove in the wall of the socket b, from itsposition shown in Fig. 5 to its position shown in Fig. 6, as the deviceH is rotated to move the lower end of the section I) held by the deviceH into engagement with the upper end of the upper section of theelectrode B. The thread pitch difference required for the purpose,depends upon, and can be readily calculated, or predetermined, as willbe apparent, from the thread pitch and thread angle "of the electrodesection and pin threads.

With the described difierence between the thread pitch of. the parts Hand H 'and the thread. pitch of the partsb and'b the rotation of thedevice H to lower the new section pin 1) from its position shown in Fig.5 to that shown in Fig. 6, will not increase the pressure between thethread on the pin. 17 and the wall thread of the socket b in the upperend of the electrode B, thus avoiding the tendency to crush or shear offthe edge portions of the threads which would result from the describedchange in relative electrode and section positions, if there were nosuch pitch difference. It is readily possible to arrest the cranelowering movement'of the device H with the electrode parts-in thepositions shown in Fig. 5, and without creating a contact pressurebetween the pin and socket threads which is objectionablylarge.

As the member H is being rotated to bring the parts into their positionsshown in Fig. 7, air under pressure is discharged through the valvedoutlet H then open for the purpose, into the narrowing jointspacebetween' the lower end of the section I) held by the device H andthe upper end of the electrode B. In the arrangement shown, the air isthus discharged into the joint space through nozzles K and K widelydisplaced from one another about the axis of the device H, and connectedto the valve outlet H' by separate horizontally disposed branch pipes Kand K respectively; As shown, the nozzles K and K are arranged todischarge jets directed radially inward toward the axis of the device Hand electrode section b held by it, at approximately the level of theannular lower end surface of said section b. With the nozzles located'as described, the annular lower end surface of the electrode section band the opposing upper end surface of the electrode B, are veryeffectually cleaned by the cleaning jets which revolve about theelectrode axis as the joint space is being closed.

After the parts are brought into the position shown: in Fig. 7, thelevers J of the lower clamping section HC are given counterclockwiseadjustments about their pivots J to thereby clamp the electrode sectionHC firmly to the upper end of the electrode B. Advantageously and asshown, the device H is so proportioned that the levers J grip the upperend of the electrode B at a distance below the upper end of theelectrode, which is equal to the distance above the lower end of sectionb in the device H, engaged by the levers I.

With the upper end of the electrode B gripped by the clamping device HCand with the lower end of the electrode section b gripped by theclamping device HlB, the clamping device HE is given a small clockwiseangular adjustment relative to the clamping device 'HC to therebyestablish the desired contact pressure between the engaging ends of theelectrode B and said section b. As previously stated in the preferredform of the present invention, this relative angular movement of the twoclamping devices is effected without the transmission of any significantstress from th clamping device HC through the electrode B to which it isclamped to the supporting gallows C for the latter. To avoid such stresstransmission, opposing torques are directly impressed on the clampingdevices HB and HG. To

this end, in the construction illustrated, the devices HB and HC areconnected by a sort of planetary gear connection.

Asshown in Figs. 1-9, the gear connection comprises a spur gear sector Lcoaxial with the device H and carried by the portion H of the device HC,and comprises a spur gear L, which is'in mesh with the gear sector L,and is carried by a. vertical shaft L journalled in the clamping frameof the device HB. The shaft L is provided at its upper end with a head Lof polygonal outline in cross section, for engagement by a manuallyactuated wrench. The latter need not be illustrated or described, as itmay be of any known or suitable form, and in particular, may well be awrench of known type, including provisions for indicating its operatingtorque. By means of a wrench having a lever handle of suitable length,and with gears L and L of suitable pitch, a workman may readily subjectthe devices HB and HC to the opposing torques needed to establish theelectrod joint pressure required for the purposes of the presentinvention.

Obviously other gear connections between the sections HB and HC may beemployed. For example, each section supports a coaxial bevel gear andeach of those bevel gears may be in mesh in a known manner with aninterposed bevel gear having its axis radial to the axis of the firstmentioned bevel gears.

When conditions make it desirable, the tightening connection between theupper and lower clamping devices may b motor actuated. Thus, in themodified form of tightening device I-ID shown in Fig. 10, an electricmotor M carried at one side ofthe device, rotates a vertical shafthaving a lower portion journalled in the upper clamping device hb, andcarrying a spur gear L in mesh with a spur gear sector L carried by thelower clamping section he. Each of the sections hb and he is shown as acomplete annulus, but this is not essential to the use of the motor, andotherwise sections hb and he are generally similar in construction andoperation with the previously described sections HC and HB. As shown,the device HD includes another gear sector L and gear L the latter beingcarried by a short shaft L with its upper end shaped for engagement by awrench, whereby the device HD has the same capacity for manual operationas does the previously described device H.

The tightening device HD may also include suspensionportions.correspondingportion of the device H. A shown, however, thedevice I-ID does not include the air reservoir tank portion of thedevice H, but is-formed' by vertically disposed bars or frame members H,which have inclined upper end portions included in the suspensionsection of the device 1-11). In lieu of such a tank portion, the deviceHD includes a blower N mounted above and driven by the motor M, andthrough a pipe N supplying air under pressure to one or more cleaningnozzles K which may be similar in form and disposition to the nozzles Kand K of the construction first described.

As will be apparent from the. foregoing, the general operation of theapparatus shown in Figs; 1-9, comprises the following steps: The initialinsertion of the threaded suspension device E in one end of an electrodesection b, usually while the latter i horizontally disposed in such astock pile of such electrode sections as is shown in Fig;

' 1. Usually at the same time at whichthe mem-- ber E is threaded intoone end of a section b, a connecting pin or nipple b is threaded intothe other end of the section. The device E is then engaged by the craneor hoist hook F which moves the electrode section into position upon thesupport G as shown in Fig. 3. The member E i then screwed out of theupper end of the section b and the latter is clamped to device If bysuitable adjustment of the clamping-levers I.

The device H is then moved by the hook F into the position to bringsection b above the electrodeB of the furnace A to which said section bis to be added. The device H is then lowered to enter the pin 1) of thesection b into the socket b in the upper end of the electrode B,generally as shown in Fig. 5. The member H is then rotated to lower thenut part H relative to the suspension bolt H and thu moves the section17 into the position relative to the electrode B in which the abuttingends of the section and electrodes are in engagement as shown in Fig. 6.The levers J are then turned counterclockwise to clamp the clampingsection HC to the upper end of the electrode B. The gear shaft L is thenrotated in the clockwise direction, as seen in Figs. 8 and 9,

to establish the desired contact pressure between the electrode sectionsrespectively clampedto the clampingsections HB and HC of the clampingdevice.

The foregoing operation complete the operation of connecting anelectrode section to a furnace electrode, and is followed by therotation of thelevers I and J counterclockwise and clockwise,respectively, to release the clamping devices HB and HC of the device Hwhich is then moved away p;

from the furnace. In the ordinary use of the invention, the supply ofcurrent to the furnace electrodes will be interrupted during the periodin which the electrode section engaged by the tightening device is beinglowered into engagement with the furnace electrode and during thesubsequent joint tightening operation.

As the section held by the tightening device is being lowered intoengagement with the furnace electrode, compressed air is discharged intothe joint space to blow dirt off the electrod surfaces which are to bebrought into engagement. When the compressed air is supplied from areservoir It included in the tightening device a shown in Figs. l-9, theplant station at which the support G is located, preferably includes acompressor for other source of compressed air with a discharge hose 0conveniently disposed to permit the reservoir space to be recharged eachtime the device H is moved into the position shown in Fig. 4. With suchfrequent recharging, the volumetric capacity of the reservoir h, doesnot need to be great enough to involve objectionable increase in thebulk of the tightening device H, or to require the safety provisions andattention needed with compressed air reservoirs of greater volume. Inthe actual operation of coupling an electrode section B held by thedevice H to a furnace electrode, the joint cleaning operation requiresno attention from the attendant other than the mere opening and closingof th valved outlet H.

With the form of the invention shown in Fig. 10, the joint cleaningoperation requires that the motor M driving the blower N be operatedduring the period in which an electrode section b is being moved fromthe general position relative to the furnace electrode shown in Fig.into the position shown in Fig. 6. As those skilled in the art willunderstand, the shaft M normally will be connected to the armature shaftof the motor M through a suitable speed reduction gear M Advantageously,the motor M may be of a known commercial type, adapted to automaticallystall when the motor torque increases to the value corresponding to thepredetermined contact pressure desirably established between theelectrode sections clamped to the upper and lower clamping sections hband hc.

In the'diagram shown in Fig. 11, the curve P illustrates the variationsin the resistance of an electrode joint between two end to'end sectionsb of an electrode coupled, as hereinbeforedescribed, as the contactpressure between the'two sections is increased. In Fig. 11, theabscissae unit is a torque foot pound, and the ordinates unit is an ohm.The curve P shown in Fig. 11 is based upon and corresponds to dataobtained in tests made on graphite furnace electrode sections 18 indiameter in which use was made of a joint tightening device constructedand operated in accordance with the present invention, to establish highcontact pressures between the elec-' trode sections. As the curve Pshows, a great reduction in the joint resistance is obtained byincreasing the maximum joint tightening torque in the case of a graphiteelectrode of standard construction and 18 in diameterfrom the limit ofabout 300 foot pounds, heretofore customary, up to about'3000 footpounds.

The general advantages of the present invention may be attained with anelectrode contact pressure varying froma minimum appreciably above thatheretofore customary, to a maximum but little below the safe'crushingstrength of the electrode material. While the joint resistance continuesto diminish as the joint tightening force increases, the curve P isasymptotic, and the decrease in joint resistance as the torque isincreased substantially above 3000 foot pounds, is relatively small andordinarily will not justify the increase in the power of the tighteningdevice required, and the resultant increase in the risk of injuring theelectrode sections.

The general operation of the apparatus shown in Fig. 10 is the same asthat of the apparatus shown in Figs. l-9, except in respect to the jointcleaning action, and except as a result of the fact that each of themembers hb and be is a complete annulus. While the formation of each ofthe clamping sections hb and he shown in Fig. 10 as a complete annulus,permits of some reduction in the weight of metal required to giveadequate strength to said sections, a tightening device including suchannular clamping sections has the practical disadvantage that it must bemoved longitudinally relative to the electrodes and electrode sections,into and out of operating relation with the latter. A tightening deviceopen at one side as in the form first described, can be moved laterallyinto and out of engagement with furnace electrodes and sections, andhence has the advantage of requiring appreciably less crane elevationand head room than are required with the construction shown in Fig. 10.

While in accordance with the provisions of the statutes, I haveillustrated and described the best forms of embodiment of my inventionnow known to me, it will be apparent to those skilled in the art thatchanges may be made in the form of the apparatus disclosed withoutdeparting from the spirit of my invention as set forth in the appendedclaims and that in some cases certain features of my invention may beused to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

, 1. A device for connecting anelectrode section to the upper and outerend of a furnace elec trode having a tapered, internally threaded, axialsocket at said end, said electrode section having at its lower end atapered, externally threaded, axially disposed pin portion adapted to bethreaded into said socket, said device comprising clamping means forengaging and gripping said electrode section and comprising suspensionmeans including a nut portion coaxial with. and above an electrodesection engaged and gripped by said clamping means and comprising a boltthreaded into said nut, said bolt and nut portion having a thread pitchfiner than the thread pitch of said socket and pin, by such apredeterminable amount, that when said section and clamping element aresuspended with said pin entered in said socket and the nutand boltelements are rotated relative to one another to lower said pin into saidsocket, the pin thread surface may engage and slide along the threadsurface of the socket, without transferring any substantial portion ofthe weight of said device and electrode section to the electrode.

2. Apparatus for establishing a threaded connection between end to endsections of an electrode comprising a gauging element having a seatadapted to be engaged by the lower end of an electrode section and tosupport the latter, and formed with device supporting means inpredetermined relation to said seat, and a device adapted to engage and.be supported by said means :and comprising clamping means adaptedfor'gripping engagement-with an electrode section supported by saidseatsurface and comprising other clamping meansspaced from the firstmentioned clamping means and rotatable relative to the first mentionedclamping means and adaptedto engage andtclamp a second electrode sectionin end to end relation with the first mentioned section.

3. A device adapted for use in establishing a threaded connectionbetweensections of a cylindrical carbon electrode and comprising aclamping section including clamping means adapted to engage an electrodesection at points displaced about its axis, a second clamping sectionconnected to and supported by thefirst mentioned clamping section, andadjustable relative to the latter angularlyabout'the axis of .anelectrode section gripped by the :upper *clamping section and includingclamping means adapted to engage at points displaced about the electrodeaxis an electrode section in end :to end relation with the" electrodesection engaged by the first mentioned clamping section, means actingbetween said clamping sections and subjecting the latter to opposingtorques about their common axis and a compressed air supply tank carriedbyone of said clamping sections along side the position of an electrodesection engaged by the last mentioned clamping section, and a jointcleaning air nozzle connected to and adapted to receive air underpressure from said tank and operable to discharge a cleaning jet of airinto the'joint space between the ends .of the two electrode sections.

FRANK W. BROOKE.

